Polycystic Kidney Disease (cont.)
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How is autosomal dominant PKD diagnosed?
Autosomal dominant PKD is usually diagnosed by kidney imaging studies. The most common form of diagnostic kidney imaging is ultrasound, but more precise studies, such as computerized tomography (CT) scans or magnetic resonance imaging (MRI) are also widely used. In autosomal dominant PKD, the onset of kidney damage and how quickly the disease progresses can vary. Kidney imaging findings can also vary considerably, depending on a patient's age. Younger patients usually have both fewer and smaller cysts. Doctors have therefore developed specific criteria for diagnosing the disease with kidney imaging findings, depending on patient age. For example, the presence of at least two cysts in each kidney by age 30 in a patient with a family history of the disease can confirm the diagnosis of autosomal dominant PKD. If there is any question about the diagnosis, a family history of autosomal dominant PKD and cysts found in other organs make the diagnosis more likely.
In most cases of autosomal dominant PKD, patients have no symptoms and their physical condition appears normal for many years, so the disease can go unnoticed. Physical checkups and blood and urine tests may not lead to early diagnosis. Because of the slow, undetected progression of cyst growth, some people live for many years without knowing they have autosomal dominant PKD.
Once cysts have grown to about one-half inch, however, diagnosis is possible with imaging technology. Ultrasound, which passes sound waves through the body to create a picture of the kidneys, is used most often. Ultrasound imaging does not use any injected dyes or radiation and is safe for all patients, including pregnant women. It can also detect cysts in the kidneys of a fetus, but large cyst growth this early in life is uncommon in autosomal dominant PKD.
More powerful and expensive imaging procedures such as CT scans and MRI also can detect cysts. Recently, MRI has been used to measure kidney and cyst volume and monitor kidney and cyst growth, which may serve as a way to track progression of the disease.
Diagnosis can also be made with a genetic test that detects mutations in the autosomal dominant PKD genes, called PKD1 and PKD2. Although this test can detect the presence of the autosomal dominant PKD mutations before large cysts develop, its usefulness is limited by two factors: detection of a disease gene cannot predict the onset of symptoms or ultimate severity of the disease, and if a disease gene is detected, no specific prevention or cure for the disease exists. However, a young person who knows of a PKD gene mutation may be able to forestall the loss of kidney function through diet and blood pressure control. The genetic test may also be used to determine whether a young member of a PKD family can safely donate a kidney to a family member with the disease. Individuals with a family history of PKD who are of childbearing age might also want to know whether they have the potential of passing a PKD gene to a child. Anyone considering genetic testing should receive counseling to understand all the implications of the test.
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